Part of the purpose of the Bible is to show that we all need help, that none of us is good enough to make it on our own, and it's only because of the blood of Jesus that any of us has hope. For this reason the Bible shows flaws even in its heroes.

If you're looking for heroes in the Bible, the only person you need is Jesus Christ. He is the only man in the Bible that we can say is Good.

You're asking on specific sin of killing an innocent person by an "Old Testament hero" (a patriarch, prophet, just king etc). This is quite rare in Bible. I haven't made a thorough search and I definitelly don't know all details of Old Testament by heart, but I don't remember any other case of this sin made by a just person.

But if you were asking about sins of just people in general, these were quite common. Abraham didn't wait for God's promise and had a son with Hagar, Moses beated to the rock twice, Aron made the golden calf...